1. Field of the Invention
The present invention relates to an illuminator of a line type to be used in or installed into an image reading apparatus for use in, for example, a facsimile machine, a copy machine, an image scanner, etc.
2. Description of Related Art
In machines such as facsimile machines, copy machines, image scanners, etc., as a device for reading a manuscript or image, there is applied an image reading apparatus, such as an image sensor, etc. Known types of image sensors are, for example, the reduced type, the close-contact type, the full-contact type, etc. Among them, image sensors of the contact type are normally constructed with an illuminator, an optical device of an equal power for imaging or equimultiple imaging, a sensor, and so on.
The image sensor of the close-contact type, in general, has a short light path, compared to that of the image sensor of the reduced type, thereby allowing for an apparatus of small size, and rendering unnecessary any troublesome optical adjustment, therefore there is a merit or advantage to such an image sensor in that it can be installed with ease into an apparatus. For these reasons, it has come to be applied in many apparatus, in the place of the reduced type.
The illuminator installed in the image sensor of the close-contact type must illuminate the surface of the manuscript with an intensity of illumination higher than that for enabling to read or pick up of images thereon by means of the sensor(s). The area to be illuminated by the illuminator is in a line-like shape. Specifically, it is very long in a main scanning direction (i.e., a longitudinal direction), while it may be very narrow in a sub-scanning direction thereof being orthogonal to the main scanning direction thereof. For example, in the illuminator for use in an A4 size machine which is applied to the facsimile apparatus, the length in the longitudinal direction must be 216 mm or longer. A further necessary attribute of the illuminator is uniformity of illumination. Unevenness in the illumination intensity on the surface of the manuscript, particularly in the longitudinal direction, may cause error(s) in reading of the image(s), therefore it is desirable for the intensity of illumination to be as uniform or even as possible.
As such the illuminator, conventionally, there is already known an illuminator of an LED array type, in which a few or several tens (for example, 30 pieces) of the LEDs (Light Emitting Diodes) are mounted on a printed circuit board by means of wire-bonding or soldering in a line. And, in the close-contact type image sensor being installed with such the illuminator therein, the light irradiated from the illuminator is incident upon the manuscript to be read after passing through a cover glass which functions also as a support for the manuscript, and then the light reflected from the surface of the manuscript is received by photoelectric transducer elements through a rod lens array, so as to be read as the image thereof.
In such the conventional apparatus, in which a large number of LEDs are aligned, the light being actually utilized in the process of sensing an image on a manuscript is only the portion which is incident upon a narrow reading line on the manuscript to be read, but the light falling outside of this portion is not utilized. Also, there is a method in which the illuminator is brought to be as close as possible to the manuscript to be read, to make the intensity of illumination of the line of the manuscript as bright as possible, thereby to reduce the number of the LEDs necessary to be installed, however in such a case there occurs a significant lack of evenness in the intensity of illumination. Also, in the illuminator having such a structure, there occurs a lack of evenness in the amount of light in a degree varying with a pitch of mounting of the LEDs. Further, inadequate uniformity may occur in the relative brightness of the individual LEDs used due to non-uniformity in the manufacturing thereof. Accordingly, if the number of the LEDs mounted onto an illuminator is reduced, the unevenness of the intensity and distribution of light emitted upon the reading line of the manuscript to be read becomes large.
In response to the above aspect of the design and manufacture of image reading apparatus, by the same inventors of the present invention there was proposed a technology according to which the light emitting elements (i.e., the LEDs) are provided at both end portions of a transparent body in a rod-like shape, and wherein a portion of surfaces of the transparent body is formed as a light scattering surface as, for example, in Japanese Laid-Open Patent No. Hei 6-148435 (1994) and Japanese Laid-Open Patent No. Hei 7-14414 (1995).
Since the light emitting elements are provided at both end portions of the transparent body of the rod-like shape in the line illumination apparatus disclosed in those publications, it is possible to eliminate one of the provided light emitting elements. The same inventors of the present invention also proposed a line illumination apparatus wherein the light emitting element is provided only at one end portion of the rod-like transparent body as, for example, in Japanese Laid-Open Patent No. Hei 8-163320 (1996) and Japanese Laying-Open Patent No. Hei 8-172512 (1996). The line illumination apparatus disclosed in those publications can obtain a reduction of cost by arranging the light emitting element only at the one end of the rod-like transparent body, and at the same time by making the shape of the light scattering pattern which is formed on the surface of the rod-like transparent body whereby the light irradiated from the light emitting elements expands from one end, upon which the light is incident, to the other end gradually, in the area of the light scattering pattern, for the purpose of obtaining an even or uniform illumination intensity along the longitudinal direction thereof.
Previously, in Japanese Laid-Open Patent No. Hei 7-183994 (1995), there was disclosed an image reading apparatus having an illumination means, which has at least two light sources each being different in the light emitting wavelength thereof, wherein the light sources are disposed with their alignments being shifted from a normal line passing through a center of a scattering and reflection region, so that the light comes to be incident in a uniform amount upon the scattering and reflection region, in the longitudinal direction thereof.
Further, the same inventors of the present invention disclosed the following, in Japanese Laid-Open Patent No. Hei 10-126581 (1998).
Namely, in a line type illuminator being provided with a light source at one end portion, the other end portion of a light guide being a rough surface, a light scattering pattern is devised so that the incident light is consumed as the illumination light until it reaches the other (non-emitting) end portion, thereby enabling that the illumination intensity may be maintained to be high and uniform.
However, with the line type illuminator mentioned in the above, inherent problems of reading of, in particular, a color manuscript, have not been studied.
Namely, when reading the color manuscript, the light emitting elements (for example, the LEDs), each emitting light at a different wavelength (for example, wavelengths corresponding to RGB), are energized one by one, so as to detect the intensity of reflection light in the respective wavelengths by means of sensors.
Taking the minimum light source for color into a consideration, there can be considered a light source constructed with three (3) LED chips, each having a different emission wave-length. There is a need of miniaturizing the image reading apparatus. Therefore, there is also the need of miniaturizing the line type illuminator for use therein.
If applying the above-mentioned light source constructed with the three (3) LED chips, each having the different emission wave-length, in the line type illuminator which is disclosed in the above-mentioned Japanese Patent Laid-Open No. 10-126581 (1998), the following aspects may be further improved.
Depending upon the dispositions of the LEDs which are energized separately, there is a necessity for improving the uniformity of the illumination intensity, in particular in the vicinity of the light source.
This can be considered because, in the vicinity of the light source, a positional and angular relationship between the LEDs to be lit and the illumination light scattering pattern and further the former""s relationship with an outgoing surface thereof are changed. As the LED chips are of insubstantial size, it is therefore impossible to position them at substantially the same position.
An object of a device according to the present invention, with a line type illuminator that employs a plurality of light sources, each having a different light emission wave-length, the light sources are positioned only at one end of the illuminator, is to provide a inexpensive light illuminator that maintains uniformity in illumination intensity in the longitudinal direction thereof.
According to the present invention, there is provided a line type illuminator, having a scanning direction in a longitudinal direction, and a sub-scanning direction being orthogonal to the scanning direction and being narrow in a width thereof, comprising:
a light source unit being constructed with a plurality of light sources, each of which can be activated independently;
a rod-like transparent light guide, having a reflective surface opposing the light source unit at an end in the longitudinal direction thereof; and
a case, in which the rod-like transparent light guide is received, wherein the rod-like transparent light guide is formed to have a polygonal cross-section thereof, a chamfered portion formed as a light emission surface and formed in the longitudinal direction at a corner thereof, and a main light scattering pattern formed in a portion intersecting a normal line of the light emission surface and opposing thereto, wherein,
an auxiliary light scattering pattern is provided between the main light scattering pattern and the light source unit, and the auxiliary light scattering pattern is shifted outside from a center line of the main light scattering pattern in the longitudinal direction thereof, and further a normal line in a region of the auxiliary light scattering pattern intersects a center line of any one of the plurality of light sources, extending in the longitudinal direction.
And, according to the present invention, the auxiliary light scattering pattern mentioned above can be considered to be formed with two spot-like patterns which are provided separately in a width direction of said rod-like transparent light guide. However, the number of the spot-like patterns may be three (3) in total.
Also, according to the present invention, the other end surface of the above-mentioned rod-like transparent light guide may have a rough surface. Such a rough surface can be manufactured with ease, however the light incident upon the rough end surface is hardly reflected because of the rough surface thereof. A white paint is therefore applied upon the rough surface to reflect light more effectively, thereby obtaining a further utilization of the light emitted by the light sources.
Further, according to the present invention, the center line of the main light scattering pattern in the longitudinal direction thereof is shifted toward said chamfered portion from the center line of the rod-like transparent light guide, and the main light scattering pattern may have a first portion the width thereof gradually increasing from a minimum at the end where the light source unit is positioned toward a relative maximum at the other end thereof, a second portion which is continuous to said first portion and is increased in a width thereof, this width increasing in the same direction as and at a rate larger than that of said first portion, and a third portion which is continuous to said second portion and is extended toward the other end with a width being equal to a maximum width of said second portion.
With such a construction, it is possible to maintain a high intensity of illumination, and a high degree of evenness or uniformity thereof as well.
Further, according to the present invention, the first portion of said main light scattering pattern mentioned above may be formed with a portion in which light scattering patterns are formed discontinuously or spattered, and with another portion in which the light scattering patterns are formed continuously. In particular, in a case where the engaging portion in the concave and convex shape is formed in a portion of the rod-like transparent light guide, with the provision of a pattern omission portion corresponding to the concave and convex engaging portion, it is possible to maintain evenness of illumination.